Impact glass from asteroids and comets stores biodata for millions of years

Impact glass from asteroids and comets stores biodata for millions of years

Bits of plant life encapsulated in molten glass by asteroid and comet impacts millions of years ago give geologists information about climate and life forms on the ancient Earth. Scientists exploring large fields of impact glass in Argentina suggest that what happened on Earth might well have happened on Mars millions of years ago. Martian impact glass could hold traces of organic compounds.

Bits of plant life encapsulated in molten glass by asteroid and comet impacts millions of years ago give geologists information about climate and life forms on the ancient Earth. Scientists exploring large fields of impact glass in Argentina suggest that what happened on Earth might well have happened on Mars millions of years ago. Martian impact glass could hold traces of organic compounds.

Asteroid and comet impacts can cause widespread ecological havoc, killing off plants and animals on regional or even global scales. But new research from Brown University shows that impacts can also preserve the signatures of ancient life at the time of an impact.

A research team led by Brown geologist Pete Schultz has found fragments of leaves and preserved organic compounds lodged inside glass created by a several ancient impacts in Argentina. The material could provide a snapshot of environmental conditions at the time of those impacts. The find also suggests that impact glasses could be a good place to look for signs of ancient life on Mars.

The work is published in the latest issue of Geology Magazine.

The scorching heat produced by asteroid or comet impacts can melt tons of soil and rock, some of which forms glass as it cools. The soil of eastern Argentina, south of Buenos Aires, is rife with impact glass created by at least seven different impacts that occurred between 6,000 and 9 million years ago, according to Schultz. One of those impacts, dated to around 3 million years ago, coincides with the disappearance of 35 animal genera, as reported in the journal Science a few years back.

"We know these were major impacts because of how far the glass is distributed and how big the chunks are," Schultz said. "These glasses are present in different layers of sediment throughout an area about the size of Texas."

Within glass associated with two of those impacts — one from 3 million years ago and one from 9 million years ago — Schultz and his colleagues found exquisitely preserved plant matter. "These glasses preserve plant morphology from macro features all the way down to the micron scale," Schultz said. "It's really remarkable."

The glass samples contain centimeter-size leaf fragments, including intact structures like papillae, tiny bumps that line leaf surfaces. Bundles of vein-like structures found in several samples are very similar to modern pampas grass, a species common to that region of Argentina.

Scientists have worked out the characteristics of the air on Mars 3.6 billion years ago.

The work by a team of US researchers suggests that the thin atmosphere would have led to cold, dry conditions on the planet.

The results are important because they shed light on how habitable Mars was billions of years ago, and how long any surface water persisted.

Details have been published in the journal Nature Geoscience.

The scientists calculated the early Martian atmospheric pressure using patterns of ancient meteor craters and dry river beds seen on its surface today.

They used new Mars orbiter data to test out an idea first proposed by Carl Sagan more than 20 years ago – that atmospheric pressure is recorded by the size of the smallest impact craters.

The ancient Martian climate is inferred from the landscape of water-sculpted lakes and river beds seen today. They show that liquid water must have existed on its surface early in the planet’s history.

The new result, however, implies that Mars was not a permanently warm wet world and that periods of arid, sub-zero conditions existed.

River channels at Aeolis Dorsa, near Gale Crater on Mars, interweave with impact craters, and it is the smallest of these craters that are key to the new findings.

The craters sit within riverbeds thought to be about 3.6 billion years old.

On planets with a thick atmosphere, small meteors break up and burn as fireballs, never reaching the ground. But some of the craters at Aeolis Dorsa are only a few tens of metres across, suggesting that quite small meteors made it through the thin atmosphere.

Into thin air

The result raises questions about just how habitable Mars was billions of years ago, and how long any surface water persisted.

“Our work has nudged me towards thinking that the conditions were mostly very cold and very dry even on early Mars – similar to (Earth’s) Antarctic Dry Valleys today,” lead author Dr Edwin Kite told BBC News.

“However, there is still plenty of microbial life even in the Antarctic Dry Valleys so our work doesn’t rule out an early environmental niche for life on Mars.”

Although this method for measuring limits of atmospheric pressure on Mars was suggested a couple of decades ago, it has only recently become possible with the advent of high resolution images of the surface from extended missions like Nasa’s Mars Reconnaissance Orbiter.